System for remote testing of telephone subscribers{3 {0 lines

ABSTRACT

A remotely controlled telephone loop testing system is disclosed in which the loop test circuits are set up by multifrequency tone bursts from the controlling station. The direct current in the remote loop is transmitted back by being translated into a variable frequency signal which is retranslated to direct current at the control station, and displayed on a meter. All signalling is over nondedicated trunks, and a gate is provided to cut off the variable frequency signal when multifrequency signals are detected on the trunk.

United States Patent SYSTEM FOR REMOTE TESTING OF TELEPHONE SUBSCRIBERS LINES 3 Claims, 26 Drawing Figs.

US. Cl 179/175.2, 179/1 6, 340/207 Int. Cl H04m 3/22, H04q 9/12 NEAR ow OFFICE we LOCAL I LOOPS I NEAR END SWITCHING SVSTENI [50] Field of Search 340/207; I 79/1 75.2

[ 56] References Cited UNITED STATES PATENTS 3,387,296 6/ 1968 Epstein et al. 340/207 Primary Examiner-William C. Cooper AttorneysR. J. Guenther and William L. Keefauver ABSTRACT: A remotely controlled telephone loop testing system is disclosed in which the loop test circuits are set up by multifrequency tone bursts from the controlling station. The direct current in the remote loop is transmitted back by being translated into a variable frequency signal which is retranslated to direct current at the control station, and displayed on 4 a meter. All signalling is over nondedicated trunks, and a gate is provided to cut off the variable frequency signal when multifrequency signals are detected on the trunk.

, mzmoomcs l LOCAL I LOOPS l9 l a *J, i 5; 50 x2 uou- DEDICATED TRUNKING 3 FACILITIES in Pate nteid Marh 16, '1971 20 Sheets-Sheet 5 NEAR END TEST TRUNK CIRUIT FIG. 9

MULTIFREQUENCY com; GENERATOR v co(195o-) K456 W 3%) 452' Aa(e52-) COMMON wwwm Patented March 16, 1971 3,571,530

20 Shoots-Sheet a FIG. I0 [on CYCLE RECEIVER CZESL FIG.

DETECTOR 20 Shoots-Sheet 10 MULTIFREQUENCY RECEIVER FIG. 12

FIG. I6

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PREAMPLIFIER:

(FIG.|5)

' Patented. March 16, 1971 20 Sheets-Sheet 11 TEST RELAY REGISTER OPERATE RELAYS RELEASE RELAYS FIG-13A Patented Much 16, 11971 20 Sbaets-8heet 1i y 5T 8 a! u LP. m wnw m Em H. I n. h I] W oh :x I: {31. v, uwvSmv? $9 l m G m2 $2 .m 0 X u m a 2 E? |Q| N: x 1m x 8 2 2 x muL Q E2 5Q u u x PM E E N: m d i1 SOC Q 22 m u 7 m2 o J \1 L W 1 W23 N T J A x J x W x8196 1m m a uz a? A 2 a; 3 z .E $235 1 mmw m 5 a: 2 A; "a u R 5 3 S I q 1L 5 3 E QQQSZEHE $2 SE 52 25 xoozi a 523mm 5 E.2ou x23 .Sw... wkoimm Patented March 16, 1971 i I 3,571,530

20 Sheets-Sheet 16 FIG. /.5

MuLTIFR QuENcv PRE AMPL1F|ER VA o in 'cIIANNEL SEPARATION FILTERS 67a. (FIGIZ) FIG. /6

CHANNEL AMPLIFIER ,LIMITER AND DETECTOR DET WW r728 -TO 2 CHANNEL 727 SEPARATION FILTER 725 TO OTHER 1 0ETEcToRs\ DETECTOR BIAS SUPPLY Patented March 16, 1971 3,571,530

20 Sheets-Sheet 1? FIG. /7 GATE GENERATO B TO GATE 638 FIG. /8 SUEERVISORY QSCILLATOR TO LINE 806 AMP.3|O

so? was) Patented March 16; 1971 I 3,571,530

20 Sheats-Shee t 19 FREQUENCY III'I VARIABLE TO AUDIO GATE 308 (FIG 5) .I I I I I I I I I I I :mrr:

m "WIT INVERTER 

1. A telemetering system for direct current signals comprising means for detecting the flow of direct current in a telephone subscriber loop, means for translating the magnitude of said direct current flow into a variable frequency alternating current signal whose frequency is proportional to said magnitude, transmitting station means for transmitting said variable frequency alternating current signals to a remote receiver over a nondedicated trunk facility, said nondedicated trunk facility also being available for the transmission of multifrequency tone signals between said transmitting station means and said remote receiver, means for detecting the presence of prescribed multifrequency tone signals on said nondedicated trunk facility, audio gate means for interrupting the transmission of said variable frequency alternating current signals during such time as said prescribed multifrequency tone signals appear on said trunk facility so that said variable frequency alternating current signals do not interfere with said multifrequency tone signals, means at said receiver for producing a direct current signal proportional to the frequency of said variable frequency alternating current signal, and means for displaying the magnitude of said last-named direct current signal.
 2. A telemetering system according to claim 1 wherein said translating means comprises a current controlled variable frequency oscillator having first and second magnetic amplifier stages for amplifying said direct current flow, and a transformer-coupled saturable core transistor oscillator circuit supplying an output frequency proportional to its supply voltage, said supply voltage being derived from the output of said second magnetic amplifier stage.
 3. The telemetering system according to claim 1 wherein said means for detecting the presence of pRescribed multifrequency tone signals comprises a plurality of detector means for furnishing voltage outputs corresponding to the presence of frequencies designated to be used for multifrequency signaling, and logical OR gate means for indicating the presence of a combination of voltage outputs from said detector means corresponding to the presence of a combination of frequencies designated as a valid multifrequency code; and wherein said audio gate means comprises a plurality of diodes in the signal path of said variable frequency alternating current signals and means for biasing said diodes into their nonconducting region in response to an indication from said logical OR gate means. 